This invention relates in general to the manufacture of tanks and in particular to a new and useful method of manufacturing a pressure tank.
In the manufacture of pressure tanks of lightweight material and composite structure, it is known to reinforce an inner tank of light metal by a back-up wrapping of filaments, threads or some tissue. This back-up wrapping relieves the inner tank of load to the effect that the sum total of pressure forces acting on the tank are taken up only partly by the inner tank, and mostly by the back-up wrapping. To minimize the weight of the tank for the given pressure and volume, an inner tank and wrapping material having as great a breaking strength as possible are to be provided.
If the load on the tank wall due to the pressure from the inside is to be taken up by both the inner tank and the wrapping, the absolute expansions of the inner tank and the wound filament must be equal to each other. For this reason, a combination of filaments having a small coefficient of thermal expansion, such as carbon fibers, with light metal inner tanks (aluminum or magnesium) are advantageously preferred in the lightweight construction.
To obtain a lightweight structure, it is sought to take up most of the load by the wrapping and as little as possible by the inner tank since the breaking strength of this tank is small. In consequence, inner tanks with very thin walls are provided. The wrapping operation is necessarily effected with prestressed filaments. The filament stress accumulated during the wrapping operation results in a load acting on the inner tank and involving the risk of breaking the thin walls of the inner tank.